Turkey Tells Soccer Fans to Toe the Line

ISTANBUL—The Turkish government's many efforts to curb dissent following the mass protests that shook the country in June have reached an unlikely new terrain: the soccer field.

The famously raucous fans of Besiktas, one of Turkey's three leading soccer clubs, must now sign a pledge when buying tickets for the season starting this month not to participate in chants during matches that could "trigger mass, political or ideological...